Recently, digital cameras which can photograph an object using a solid-state image sensing device such as a CCD (Charge-Coupled Device) array instead of a silver salt film have become popular. As for digital cameras in general, there are still cameras for still picture photography and video cameras for motion picture photography.
Recently, along with the trend toward miniaturization of CCD array elements for providing higher resolution image detection in digital cameras, there has been an increasing demand for higher resolution and shorter focal length lenses for use in these cameras. In order to miniaturize a photographic lens, in general, it can be said that xe2x80x9cthe smaller the number of lens elements, the betterxe2x80x9d. As an example of a photographic lens having a small number of lens elements, a triplet-type lens consisting of three lens elements in three lens groups is conventionally known. However, a triplet-type lens is insufficient in terms of simplicity of construction, compactness, and cost.
In Japanese Patent Publication H7-050246 a photographic lens consisting of two lens elements in two lens groups is disclosed. It consists of, in order from the object side, a meniscus lens element of negative refractive power and a biconvex lens element, wherein one lens surface is made to be aspherical. However, this photographic lens is unsuitable for use in a compact, digital camera. For example, in a compact, digital camera loaded with a CCD array that is about 2 mm in diameter, the distance from the first lens surface to the image surface must be about 3 mm or less. The photographic lens described in the Japanese Patent Publication H7-050246 is not compact enough to meet such a requirement.
The present invention relates to a photographic lens used in a digital camera. More particularly, the present invention is a single focus lens that is suitable for use as the main lens of a highly portable, compact digital camera.
The object of the present invention is to provide a single focus lens that has a simple construction and an overall length that is sufficiently short for use in a compact digital camera.